Click Comparison of Digital and Matched Filter Receivers

The concept of clicks in an FM receiver was originally used by S. O. Rice 1 and J. Cohn 2 to explain the effect of noise on analog signal demodulation near threshold. Recently, several theoretical investigations of digital FSK signal demodulation have applied the concept of clicks in analyses of low pass filter processing of the discriminator output. Klapper, 3 and Mazo and Salz 4 modelled the low pass filter with an integrate-and-dump function, while Schilling, Hoffman, and Nelson considered a gaussian low pass filter. 5 In all cases, additive gaussian noise was assumed to be the sole source of interference in the signal channel. In this paper, we consider intersymbol interference that is induced by delay dispersion in the signal channel. Analysis is limited to a practical single-echo channel* and binary orthogonal modulation. Although the analysis seems to be tractable for only special cases, we gain insight into the error mechanism of digital FM reception. The relation between clicks and errors is viewed as follows. Since the fundamental description of clicks concerns a random angular encircle* The single-echo channel was used by Bennett, Curtis, and Rice 8 in their stud}' of analog angle modulated transmission systems. 301